1. Field of the Invention
The present invention generally relates to projecting images onto a projection surface such as a screen or the like, and, more particularly, to correcting distortion of such images.
2. Description of the Related Art
It is generally known to project a two-dimensional image on a projection surface, such as a screen, based on oscillating a pair of scan mirrors in mutually orthogonal directions to scan a laser beam over a raster pattern of scan lines. However, the known image projection systems project the image with limited resolution, typically less than a fourth of video-graphics-array (VGA) quality of 640×480 pixels, and with some image distortion primarily caused by the orientation of the screen relative to the image projection system.
For example, when an image having a square or rectangular image area is projected on a tilted screen that is inclined relative to an optical axis along which the image is projected, then the projected image suffers a trapezoidal or quadrilateral distortion known in the art as a “keystone” distortion. In other words, there are scan lines located further away from the image projection system which are longer in length as compared to scan lines located closer to the image projection system.
As another example, the screen may be centrally oriented perpendicular to the optical axis of the image projection system. If the projection angle is very wide, then the scan lines at the top and at the bottom of the image area will be longer than the scan lines in the middle of the image area. This is generally known in the art as side-to-side or east-to-west “pincushion” distortion.
Such pincushion or keystone distortion is generally corrected in the art by electronically clipping or cropping triangular sections of the image area in order to make the image area square or rectangular. However, when this is done, the image resolution suffers due to the loss of usable pixels.